U.S. patent application number 10/596691 was filed with the patent office on 2007-10-04 for mixer arrangement.
Invention is credited to Henrik Sjoland, Fredrik Tillman.
Application Number | 20070230558 10/596691 |
Document ID | / |
Family ID | 34486167 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070230558 |
Kind Code |
A1 |
Sjoland; Henrik ; et
al. |
October 4, 2007 |
Mixer Arrangement
Abstract
A quadrature connected passive mixer arrangement for frequency
converting analog signals from a first to a second frequency. The
arrangement comprises two parallel connected mixers provided as
transistors. First and second LO signals and their inverse signals
having separated phases are provided for driving the transistors.
Signal path switches are provided between the RF terminals and the
mixer transistors. The switches are driven by signals having a
different phase than the signal driving the corresponding mixer
transistor. Thus, any short circuit between IF terminals of the
arrangement may be eliminated.
Inventors: |
Sjoland; Henrik;
(Loddekopinge, SE) ; Tillman; Fredrik; (Lund,
SE) |
Correspondence
Address: |
ERICSSON INC.
6300 LEGACY DRIVE
M/S EVR 1-C-11
PLANO
TX
75024
US
|
Family ID: |
34486167 |
Appl. No.: |
10/596691 |
Filed: |
December 10, 2003 |
PCT Filed: |
December 10, 2003 |
PCT NO: |
PCT/EP04/13000 |
371 Date: |
March 8, 2007 |
Current U.S.
Class: |
375/235 |
Current CPC
Class: |
H03D 7/165 20130101;
H03D 7/1441 20130101; H03D 7/1458 20130101; H03D 2200/0047
20130101; H03D 7/1466 20130101; H03D 2200/0084 20130101 |
Class at
Publication: |
375/235 |
International
Class: |
H03D 7/14 20060101
H03D007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2003 |
EP |
03028350.1 |
Claims
1.-29. (canceled)
30. A quadrature mixer arrangement for converting a first signal at
a first frequency to a second signal at a second frequency, the
arrangement having a first mixer operatively coupled to a first and
a second terminal, wherein the first terminal is a positive
radio-frequency terminal and the second terminal is a negative
radio-frequency terminal; and a second mixer coupled in parallel
with the first mixer and operatively coupled to the first and
second terminal, wherein the first mixer is arranged to be
conductive for a first and/or a second state of a first mixing
signal, and arranged to mix the first signal with the first mixing
signal to provide the second signal; and the second mixer is
arranged to be conductive for a first and/or a second state of a
second mixing signal, and arranged to mix the first signal with the
second mixing signal to provide the second signal, the arrangement
comprising: a set of switch devices provided in the signal path
between the mixers and the first and second terminals, wherein
switch devices coupled to the first mixer are arranged to be
conductive for the first and/or second state of the second mixing
signal, and switch devices coupled to the second mixer are arranged
to be conductive for the first and/or the second state of the first
mixing signal.
31. The arrangement according to claim 30, wherein the first and
second mixing signals are first and second local oscillator (LO)
signals (LO.sub.I, LO.sub.Q) and/or their inverse signals, having a
common frequency and first and second phases, which are phase
shifted pi/2 radians in relation to each other.
32. The arrangement according to claim 30, wherein the first and
second mixer comprise a set of mixing means, each of the mixing
means having a first, second, and third terminal, the first mixer
adapted to be driven by the first mixing signal being an LO signal
and/or its inverse signal having first and third phases received at
the third terminals of the mixing means of the first mixer, and the
second mixer adapted to be driven by the second mixing signal being
a second LO signal and/or its inverse signal having second and
fourth phases received at the third terminals of the mixing means
of the second mixer.
33. The arrangement according to claim 32, wherein in each of the
mixers' first terminals of a first and a third mixing means of the
set of mixing means are operatively coupled to the first terminal
of the arrangement and second terminals of the first and third
mixing means are coupled to first terminals of a second and a
fourth mixing means of the set of mixing means, second terminals of
the second and fourth mixing means are operatively coupled to the
second terminal of the arrangement, and wherein IF terminals are
provided at the second terminals of the first and third mixing
means.
34. The arrangement according to claim 33, wherein the mixing means
are provided by transistors, and wherein the first and fourth
mixing means of the first mixer are adapted to be driven by the
first mixing signal, the second and third mixing means of the first
mixer are adapted to be driven by the inverse signal of the first
mixing signal, and wherein the first and fourth mixing means of the
second mixer are adapted to be driven by the inverse of the second
mixing signal, the second and third mixing means of the second
mixer are adapted to be driven by the second mixing signal.
35. The arrangement according to claim 34, wherein in each mixer
first and third switch devices are provided in the signal path
between the first terminal of the first and third mixing means and
the first terminal of the arrangement, and second and fourth switch
devices are provided between the second terminals of the second and
fourth mixing means and the second terminal of the arrangement.
36. The arrangement according to claim 35, wherein the first and
fourth switch devices coupled to the first mixer are adapted to be
driven by the second mixing signal, the second and third switch
devices coupled to the first mixer are adapted to be driven by the
inverse signal of the second mixing signal, the first and fourth
switch devices coupled to the second mixer are adapted to be driven
by the first mixing signal, and the second and third switch devices
coupled to the second mixer are adapted to be driven by the inverse
signal of the first mixing signal.
37. The arrangement according to claim 30, wherein the set of
switch devices is provided by transistors.
38. The arrangement according to claim 30, wherein the mixers
and/or the set of switch devices comprise a voltage controlled
switch.
39. The arrangement according to claim 30, wherein the mixers
and/or the set of switch devices comprise FET transistors.
40. The arrangement according to claim 39, wherein the FET
transistors are provided in CMOS technology.
41. The arrangement according to claim 30, wherein the arrangement
is provided as a transmitter mixer, the first signal is a
quadrature IF signal to be received as an input signal, and the
second signal is an RF signal to be provided as an output
signal.
42. The arrangement according to claim 30, wherein the arrangement
is provided as a receiver mixer, the first signal is an RF signal
to be received as an input signal, and the second signal is a
quadrature IF signal to be provided as an output signal.
43. The arrangement according to claim 30, implemented in a
wireless communication device having a communication interface for
wirelessly communicating with a remote communication device.
44. The arrangement of claim 43, wherein the device is one selected
from the group consisting of a portable radio communication
equipment, a mobile radio terminal, a pager, a communicator, an
electronic organizer, and a smartphone.
45. The arrangement according to claim 43, wherein the device is a
mobile telephone.
46. A method of mixing signals for converting a first signal at a
first frequency to a second signal at a second frequency having the
steps of receiving the first signal; mixing the first signal in a
mixer arrangement comprising a first and a second mixer coupled in
parallel to provide the second signal, each mixer being coupled to
a first and a second terminal, wherein the first terminal is a
positive radio-frequency terminal and the second terminal is a
negative radio-frequency terminal, by controlling the first mixer
to be conductive for a first and/or a second state of a first
mixing signal for mixing the first signal with the first mixing
signal to provide the second signal; and controlling the second
mixer to be conductive for a first and/or a second state of a
second mixing signal for mixing the first signal with the second
mixing signal to provide the second signal, comprising the step of:
controlling a set of switch devices provided in a signal path
between the mixers and the first and second terminals to
operatively couple either the first or the second mixer to the
first and second terminals by controlling switch devices coupled to
the first mixer to be conductive for the first and/or the second
state of the second mixing signal; and controlling switch devices
coupled to the second mixer to be conductive for the first and/or
the second state of the first mixing signal.
47. The method according to claim 46, wherein the first and second
mixing signals are first and second local oscillator (LO) signals,
and/or their inverse signals, having a common frequency and first
and second phases, which are phase shifted pi/2 radians in relation
to each other.
48. The method according to claim 46, comprising the steps of
providing a set of mixing means in each of the first and second
mixer, wherein each of the mixing means has a first, second, and
third terminal, driving the first mixer by using the first mixing
signal being a first LO signal and/or its inverse signal having
first and third phases received at the third terminals of the
mixing means of the first mixer, and driving the second mixer by
using the second mixing signal being an LO signal and/or its
inverse signal having second and fourth phases received at the
third terminals of the mixing means of the second mixer.
49. The method according to claim 48, further comprising the steps
of for each of the mixers operatively coupling a first terminal of
a first and a third mixing means of the set of mixing means to the
first terminal of the arrangement and a second terminal of the
first and third mixing means to first terminals of a second and a
fourth mixing means of the set of mixing means, operatively
coupling a second terminal of the second and fourth mixing means to
the second terminal of the arrangement, and providing IF terminals
at the second terminals of the first and third mixing means.
50. The method according to claim 49, further comprising the steps
of providing the mixing means as transistors, driving the first and
fourth mixing means of the first mixer by using the first mixing
signal, driving the second and third mixing means of the first
mixer by using the inverse signal of the first mixing signal,
driving the first and fourth mixing means of the second mixer by
using the inverse of the second mixing signal, and driving the
second and third mixing means of the second mixer by using the
second mixing signal.
51. The method according to claim 50, comprising the steps of for
each mixer providing the first and third switch devices in the
signal path between the first terminal of the first and third
mixing means and the first terminal of the mixer arrangement, and
second and forth switch devices between the second terminals of the
second and fourth mixing means and the second terminal of the mixer
arrangement.
52. The method according to claim 51, comprising the steps of
driving the first and fourth switch devices coupled to the first
mixer by using the second mixing signal, driving the second and
third switch devices coupled to the first mixer by using the
inverse signal of the second mixing signal, driving the first and
fourth switch devices coupled to the second mixer by using the
first mixing signal, and driving the second and third switch
devices coupled to the second mixer by using the inverse signal of
the first mixing signal.
53. The method according to claim 46, comprising the step of
providing the switch devices by means of a transistor.
54. The method according to claim 46, comprising the step of
providing the mixers and/or the switch devices as a voltage
controlled switch.
55. The method according to claim 46, comprising the step of
providing the mixers and/or the switch devices by FET
transistors.
56. The method according to claim 55, comprising the step of
providing the FET transistors by using CMOS technology.
57. The method according to claim 46, comprising the step of
providing the arrangement as a transmitter mixer, the first signal
being a quadrature IF signal, and the second signal being an RF
signal.
58. The method according to claim 46, comprising the step of
providing the arrangement as a receiver mixer, the first signal
being an RF signal, and the second signal being a quadrature IF
signal.
Description
TECHNICAL FIELD OF THE IVNENTION
[0001] The present invention relates to an arrangement for mixing
analog signals, and more particularly to a mixer arrangement for
converting a first signal having a first frequency to a second
signal having a second frequency.
DESCRIPTION OF RELATED ART
[0002] A mixer for frequency translating a signal having a first
frequency, such as a radio frequency (RF), to a signal having a
second frequency, such as an intermediate frequency (IF), is
provided in a wide variety of implementations, such as in radio
transceiver front-ends. Bluetooth.RTM. is a communication standard
where the major goal has been to remove cable connections between
electrical equipment. One area, where Bluetooth.RTM. is of
particular interest, is communication involving portable equipment,
such as mobile terminals. The terminals may also be adapted to
communicate according to e.g. a telecommunication technology, such
as GSM, UMTS, cdma2000, PCS, DCS etc. A mixer may be necessary for
the radio transceiver front-end of the Bluetooth.RTM. radio and the
telecommunication radio.
[0003] In portable communication equipment, low power solutions for
all electronic components are important. Thus, the tendency in
integrated circuit design is to apply low supply voltage for e.g.
the mixer. Also, it is often required that the implementation of
the mixer is cheap. MOS (Metal Oxide Semiconductor) technology
offers a solution, with which is possible to implement fully
integrated mixers. However, it is essential to find circuit
architectures capable of high performance at supply voltages at or
below 2V.
[0004] In modern radio communication architectures, such as
direct-conversion and low-IF, quadrature mixers are needed. A
suitable mixer topology at low voltage and low (or zero) IF
frequency is the passive quadrature mixer, which is well suited for
implementation in CMOS technology. This topology is suitable for
low voltage due to the lack of stacked transistors, and for low IF
frequencies due to the absence of flicker noise.
[0005] FIG. 1 illustrates a passive mixer, which is known in the
art. Two passive mixers comprising four CMOS transistors each are
connected in parallel and operated in quadrature. Thus, each
transistor will be active when a local oscillator (LO) signal at
its gate has a positive value. Each mixer is connected to provide
signal paths from RF terminals to first and second IF terminals
through transistors controlled by a common LO signal. At the IF
terminals first and second IF signals IF.sub.I, IF.sub.Q are
provided. The first mixer is operated by a first LO signal
LO.sub.I.sup.+ and its inverse signal LO.sub.I.sup.- having a first
phases .quadrature. and .quadrature.+.pi. radians, respectively.
The second mixer is driven by a second LO signal LO.sub.Q.sup.+ and
its inverse signal LO.sub.Q.sup.- having a second phase
.quadrature.+.pi./2 and .quadrature.+3.pi./2 radians, respectively.
In operation, two LO signals will have positive values
simultaneously. Although the transistors are operated such that the
IF terminals are generating the IF signals alternately, a path
(short circuit) is created between the IF terminals of the two
mixers when any two LO.sub.I and LO.sub.Q signals are high. This is
e.g. the case when LO.sub.I.sup.+ and LO.sub.Q.sup.+ have positive
values simultaneously. This is a problem as the undesired paths
between the IF terminals will ruin the gain of the mixers.
[0006] In the known art, the problem with the undesired short
circuits has been solved by providing resistors between the RF
terminals and each of the mixers, wherein the impedance in the
paths between the IF terminals increases. However, this introduces
another problem as it will also introduce additional noise. This is
particularly severe for low voltage circuits.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a
quadrature mixer arrangement comprising two mixers for converting a
signal having a first frequency to a signal having a second
frequency. More specifically, it is an object of the invention to
provide a mixer arrangement comprising two quadrature mixers, which
are isolated from each other without substantially effecting the
noise performance of the arrangement. Moreover, it is an object of
the invention to provide a mixer arrangement that is suitable for
implementation using MOS technology.
[0008] According to a first aspect of the invention, the above
objects are achieved by a quadrature mixer arrangement for
converting a first signal at a first frequency to a second signal
at a second frequency. The arrangement comprises input means for
receiving the first signal and output means for outputting the
second signal. A first mixing means is connected a first and a
second terminal for inputting or outputting the first or second
signal. A second mixing means is connected in parallel with the
first mixer and connected to the first and second terminals. A set
of switch devices is provided in the signal path between the mixers
and the first and second terminals. Thus any short-circuit path
occurring when the mixing means are at least partly conducting
simultaneously may be eliminated.
[0009] The first mixer may be arranged to be conductive for a first
and/or a second state of a mixing signal and to mix a first input
signal with a first mixer signal to provide a first output signal.
The second mixer is connected in parallel with the first mixer, and
may be arranged to be conductive for a first and/or a second state
of a second mixer signal. Furthermore, the second mixer is arranged
to provide a second output signal in quadrature to the first output
signal. The mixers are connected to common first and second RF
terminals of the arrangement. When transistors of the mixers are
conducting simultaneously a path is created between a first and a
second IF terminal. The set of switch devices interrupts any
potential short-circuit path between the IF terminals.
[0010] The first and second mixing signals and their respective
inverse signals are provided by four local oscillator (LO) signals,
which are phase shifted .pi./2 radians in relation to each
other.
[0011] The first and second mixers may comprise a set of mixing
means, each having a first, second, and third terminal. The first
mixer is adapted to be driven by a first LO signal and its inverse
signal having a first and a third phase, respectively, received at
the third terminals of the mixing means of the first mixer. The
second mixer is adapted to be driven by a second LO signal and its
inverse signal having a second and a fourth phase, respectively,
received at the third terminals of the mixing means of the second
mixer.
[0012] In each mixer, first and second switch devices may be
provided in the signal path between the first terminals of the
first and the third mixing means and the first RF terminal.
Similarly, third and forth switch devices may be provided between
the second terminals of the second and fourth mixing means and the
second RF terminal. Thus any short circuit between the IF terminals
may be avoided.
[0013] The mixers and/or the switch devices may comprise FET
transistors provided in CMOS technology.
[0014] The mixer arrangement may be provided either as a
transmitter or receiver mixer. In a transmitter mixer, a quadrature
IF signal will be provided as input signal and an RF signal as
output signal. In a receiver mixer, an RF signal will be provided
as input signal, and a quadrature IF signal will be provided as
output signal.
[0015] According to a second aspect of the invention, a wireless
communication device having a communication interface for
wirelessly communicating with a remote communication device,
comprising the mixer arrangement according to the invention
achieves the objects of the invention.
[0016] The device may be a portable radio communication equipment,
a mobile radio terminal, a mobile telephone, a pager, a
communicator, an electronic organizer, or a smartphone.
[0017] According to a third aspect of the invention, a method of
mixing signals for converting a first signal at a first frequency
to a second signal at a second frequency achieves the objects of
the invention. The method comprises the steps of receiving the
first signal, and mixing the first signal in a first and a second
mixing means connected in parallel to a first and second terminal
to provide the second signal. A set of switch devices provided in a
signal path between the mixers is controlled to operatively connect
either the first or the second mixer to the first and second
terminals.
[0018] The first mixing means may be controlled to be conductive
for a first and/or a second state of a first mixing signal for
mixing the first signal with a first mixing signal to provide the
second signal. The second mixer may be controlled to be conductive
for a first and/or a second state of a second mixing signal for
mixing the first signal with the second mixing signal to provide
the second signal. Switch devices connected to the first mixer may
be controlled to be conductive for the first and/or the second
state of the second mixing signal, and switch devices connected to
the second mixer may be controlled to be conductive for the first
and/or the second state of the first mixing signal.
[0019] Further embodiments of the invention are defined in the
dependent claims.
[0020] It is an advantage of the invention that the IF short
circuit paths between the parallel connected mixers of the
invention are eliminated. Furthermore, it is an advantage that the
noise performance compared with the known art is substantially
improved such that the mixer arrangement is well suited for
implementation in MOS technology and may be adapted for low supply
voltage and low (or zero) IF frequency.
[0021] It should be emphasized that the term "comprises/comprising"
when used in this specification is taken to specify the presence of
stated features, integers, steps or components but does not
preclude the presence or addition of one or more other features,
integers, steps, components or groups thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Further objects, features, and advantages of the invention
will appear from the following description of several embodiments
of the invention, wherein various aspects of the invention will be
described in more detail with reference to the accompanying
drawings, in which:
[0023] FIG. 1 is a block diagram of a prior art mixer
arrangement;
[0024] FIG. 2 is a front view of a mobile telephone and the
environment in which it may operate;
[0025] FIG. 3 is a block diagram of a the mixer arrangement
according to the invention; and
[0026] FIG. 4 is a signaling scheme illustrating the local
oscillator signals for controlling the mixer arrangement.
DETAILED DESCRIPTION OF EMBODIMENTS
[0027] FIG. 2 illustrates a mobile telephone 1 as one exemplifying
electronic equipment, in which the mixer according to the present
invention may be provided, and a possible environment in which it
may operate. The invention is not limited to a mobile telephone 1.
The invention may be provided in a wide variety of electronic
equipment wherein a mixer is required for converting a first input
signal having a first frequency to a second signal having a second
frequency. The mobile telephone 1 may comprise a first antenna 10
and a second auxiliary antenna 11. A microphone 12, a loudspeaker
13, a keypad 14, and a display 15 provide a man-machine interface
for operating the mobile telephone 1.
[0028] The mobile telephone may in operation be connected to a
radio station 20 (base station) of a mobile communication network
21, such as a GSM, UMTS, PCS, and/or DCS network, via a first radio
link 22 by means of the first antenna 10. Furthermore, the mobile
telephone 1 may in operation establish a second wireless link to a
peripheral device 30 via a second wireless link 31 by means of the
auxiliary antenna 11. The second link 31 is e.g. a Bluetooth.RTM.
link, which is established in the 2.4 (2.400-2.4835) GHz frequency
range. To establish the wireless links 22, 31, the mobile telephone
1 comprises radio resources, which are adapted according to the
relevant technologies that are used. Thus, the mobile telephone 1
comprises a first radio access means, such as a transceiver, for
communicating with the base station 20, and a second radio access
means for communicating with the peripheral device 30.
[0029] The peripheral device 30 may be any device having wireless
communicating capabilities, such as according to Bluetooth.RTM.
technology or any other wireless local area network (WLAN)
technology. It comprises an antenna 32 for exchanging signals over
the second link 31, and a transceiver (not shown) adapted according
to the communication technology that the peripheral device 30 uses.
The device may be a wireless headset, a remote server, a fax
machine, a vending machine, a printer etc. A wide variety of
electronic equipment may have such communication capabilities and
have a need for wirelessly transferring of data.
[0030] When receiving signals having radio frequencies (RF), the RF
signals may have to be down converted to a signal having a lower
frequency, such as an intermediate frequency (IF) before further
signal processing is applied. Similarly, an IF signal may have to
be up converted to a signal having a higher frequency, such as a RF
frequency, before transmitted. Thus, the radio access means of the
mobile telephone 1 may comprise one or several mixers according to
the invention for converting a signal having a first frequency to a
signal having a second frequency.
[0031] FIG. 3 illustrates a mixer arrangement according to the
invention. The mixer arrangement is arranged to generate
intermediate frequency signals IF.sub.I and IF.sub.Q having I and Q
phases, respectively, based on an RF signal provided at RF.sup.-
and RF.sup.+ terminals, or vice versa. The arrangement is a
balanced passive quadrature mixer arrangement comprising a first
and a second mixer 200, 300 connected in parallel and arranged to
be driven in quadrature. Each of the mixers 200, 300 comprises a
set of mixing devices 210, 220, 230, 240, and 310, 320, 330, 340.
Here the number of mixing devices of each mixer 200, 300 is four.
However, the number is only exemplary and should not be taken as
limiting the scope of the claims. The mixing means 210-240, 310-340
may comprise a FET transistor, such as a MOSFET, which may be
provided using CMOS technology. Each of the mixing means 210-240,
310-340 provides a voltage switch for enabling mixing of the RF
signal and first and second LO signals, or mixing of the IF signal
and the LO signals. The MOS transistor has true voltage switch
characteristics. Therefore, it is possible to provide switching in
the voltage domain. This makes it possible to reduce or even
eliminate the DC current flow through the transistor, and thereby
avoid the 1/f noise, which would be a problem especially for direct
conversion and low IF-receiver characteristics.
[0032] Each mixing means 210-240, 310-340 may be provided as an
NMOS transistor or a PMOS transistor. The NMOS transistor has
better switch performance than the PMOS transistor due to the
better mobility of electrons than holes. Other voltage controlled
switches, such as the junction field effect transistor (JFET) may
still alternatively be utilized as the mixing means.
[0033] The topology of the first and second mixers 200, 300 is
basically the same. Thus, a first terminal of the first mixing
means 210, 310 is operatively connected to a positive RF terminal,
which may be connected to any of the antennas 10, 11. A second
terminal of the first mixing means 210, 310 is connected to a first
terminal of the second mixing means 220, 320. A second terminal of
the second mixing means 220, 320 is operatively connected to a
negative RF terminal. A first terminal of the third mixing means
230, 330 is operatively connected to the positive RF terminal. A
second terminal of the third mixing means 230, 330 is connected to
a first terminal of the fourth mixing means 240, 340. A second
terminal of the fourth mixing means 240, 340 is operatively
connected to the negative RF terminal. Also, a connection is
provided between the second terminals of the first and third mixing
means 210, 230, 310, 330, and thus between the first terminals of
the second and fourth mixing means 220, 240, 320, 340. At said
connection, IF terminals are provided for providing, or receiving,
first and second IF signals IF.sub.I and IF.sub.Q, as will be
explained below.
[0034] Each of the mixing means 210-240, 310-340 comprises a third
terminal for receiving a signal from a local oscillator (not
shown). During operation of the mixing arrangement, the RF signal
will be mixed with mixing signals, i.e. the LO signal to provide a
down converted IF signal. In use in a transmitter arrangement, the
IF signal will be mixed with the LO signal to provide an up
converted RF signal. The mixer arrangement is driven in quadrature.
Thus, the first and fourth mixing means 210, 240 of the first mixer
200 will in operation receive a first LO signal LO.sub.I.sup.+
having a first phase .theta. and frequency at their third
terminals. The second and third mixing means 220, 230 of the first
mixer 200 will in operation receive the inverse of the first LO
signal LO.sub.I.sup.-, i.e. a LO signal phase shifted by .pi.
radians. The second and third mixing means 320, 330 of the second
mixer 300 will in operation receive a second LO signal
LO.sub.Q.sup.+ having a second phase .theta.+.pi./2 and a frequency
corresponding to the first LO signal at their third terminals. The
first and fourth mixing means 310, 340 of the second mixer 300 will
in operation receive the inverse of the second LO signal
LO.sub.Q.sup.-, i.e. a LO signal phase shifted .pi. radians in
relation to the second LO signal.
[0035] To avoid short circuit paths between the IF terminals,
signal path switches are provided between the mixers and the RF
terminals. Thus, the first mixer 200 comprises a first set of
signal path switches 250, 260, 270, 280, and the second mixer 300
comprises a second set of signal path switches 350, 360, 370, 380.
In this embodiment, the signal path switches are provided by mixing
means corresponding to the mixing means 210-240, 310-340 of the
mixers 200, 300. The first and fourth signal path switches 250, 280
of the first mixer 200 correspond to the second and third mixing
means 320, 330 of the second mixer 300. The second and third signal
path switches 260, 270 of the first mixer 200 correspond to the
first and fourth mixing means 310, 340 of the second mixer 300. The
first and fourth signal path switches 350, 380 of the second mixer
300 correspond to the first and fourth mixing means 210, 240 of the
first mixer 200. The second and third signal path switches 360, 370
of the second mixer 300 correspond to the second and third mixing
means 220, 230 of the second mixer 300.
[0036] A first terminal of the first and third signal path switches
250, 270, 350, 370 is connected to the positive RF terminal, and a
second terminal of said switches are connected to the first
terminal of the first and third mixing means 210, 230, 310, 330,
respectively. Correspondingly, a first terminal of the second and
fourth signal path switches 260, 280, 360, 380 is connected to the
second terminal of the second and forth mixing means 220, 240, 320,
320, and a second terminal of said switches is connected to the
negative RF terminal, respectively.
[0037] Third terminal of the switches 250-280, 350-380 are
connected to receive LO signals correspondingly to their
corresponding mixing means 210-240, 310-340 of the mixers 200, 300.
Thus, in this embodiment the switches will be a part of the
frequency translation from a first to a second frequency.
[0038] The mixer arrangement is arranged to achieve quadrature
mixing. Thus, two switches driven by the second LO signal LO.sub.Q
are for some time intervals conducting simultaneously as two mixing
means driven by the first LO signal LO.sub.I are conducting.
[0039] FIG. 4 illustrates the local oscillator (LO) signals
LO.sub.I.sup.+, LO.sub.I.sup.-, LO.sub.Q.sup.+, and LO.sub.Q.sup.-.
LO.sub.I and LO.sub.Q can each have a first and a second state,
i.e. a specific frequency and phase, for turning a mixing means
connected to the signal on or off. The first mixer 200 is
conductive for a first and/or a second state of the first LO signal
LO.sub.I. The second mixer 300 is conductive for a first and/or a
second state of the second mixing signal. As can be seen from the
scheme of FIG. 4, two LO signals can be positive simultaneously,
which corresponds to the gray areas. If the phases of the LO
signals are chosen as described above, LO.sub.I.sup.+ and
LO.sub.Q.sup.-, LO.sub.I.sup.+ and LO.sub.Q.sup.+, LO.sub.Q.sup.+
and LO.sub.I.sup.-, and LO.sub.I.sup.- and LO.sub.Q.sup.-,
respectively, will be positive simultaneously, as is illustrated in
FIG. 4. To avoid short circuits, the switches are therefore
arranged such that in each potential path between the IF terminals
IF.sub.I and IF.sub.Q there are at least two switches controlled by
signals having opposite phases, such as LO.sub.I.sup.+ and
LO.sub.I.sup.-, wherein there will be no risk of interference
between the IF terminals. The switches 250-280 connected to the
first mixer 200 are arranged to be conductive for the first and/or
second state of the LO or mixing signal driving the second mixer
300. The switches 350-380 connected to the second mixer 300 are
arranged to be conductive for the first and/or second state of the
LO or mixing signal driving the first mixer 200. Thus, any short
circuit between the mixers 200, 300 is avoided without
substantially introducing any noise.
[0040] The embodiment of FIG. 3 illustrates one possible
combination of providing the mixing means and the switches. There
are a number of combinations, which will achieve the same result.
Each of the switches may e.g. be interchanged with the mixing means
to which it is connected. The combination that achieves the best
performance has to be tested in each specific case and should not
be limited by the embodiment shown.
[0041] The mixer arrangement may be arranged to down convert an RF
signal received as an input signal at the RF terminals to an IF
output signal provided at the IF terminals. Alternatively, an IF
signal provided as an input signal at the IF terminals may be up
converted to an RF output signal provided at the RF terminals.
Thus, the present invention may be incorporated in either a
receiver or a transmitter for providing frequency conversion from a
first to a second frequency.
[0042] The present invention has been described above with
reference to specific embodiments. However, other embodiments than
the above described are equally possible within the scope of the
invention. Different method steps than those described above,
performing the method by hardware or software, may be provided
within the scope of the invention. The different features and steps
of the invention may be combined in other combinations than those
described. The invention is only limited by the appended patent
claims.
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